Thrombolysis is a very effective therapy for stroke patients. Instead of limiting thrombolysis within three hours after the onset of a stroke symptom, it is observed that, based on the patient's individual status, the time window of applying thrombolysis can be extended to 6 or 9 hours. This observation underscores the shift from the old concept of “Time is Brain” to the new concept of “Physiology is Brain”.
In current practice, the following protocols are widely used in the case of multi-protocol CT imaging. FIG. 1 shows the steps of a multi-protocol CT scan. First, in step S110, an nCT (native CT) is performed to check whether a hemorrhagic stroke exists; if this hemorrhagic stroke does not exist, a CTP (CT perfusion) scan is performed in step S120 to determine the physiological parameters. Then, in step S125, a saline flash is optionally performed to clean the vascular system so as to prevent the influence of a previously applied contrast agent. In step S130, a CTA (CT angiography) can be performed to determine the status of the vessels and detect the clot that causes the ischemic stroke. It is possible to change the sequence between CTP and CTA after performing nCT. In current practice, the operation of CTP is the same, no matter whether it is performed before or after CTA.
However, CTP has the drawback that it is limited to a small portion of the brain. Currently, only two or four slices of the head are acquired at a standardized position that covers the territory of the MCA (mid cerebral artery). Although most ischemic stroke lesions (about 75%) can be found in the MAC territory, about 25% of the ischemic strokes are missed from the outset.
To extend CTP to the whole brain, a method named “Neuron Perfused Blood Volume Imaging” is proposed. This method extends the spatial coverage by reducing the number of time points to exactly two, which reduce the imaging resolution. The method is still in its testing phase. Another drawback of this method is its low image resolution.